1. Field of the Invention
The present invention relates to an oscillation type angular velocity measuring device and, more particularly, to an angular velocity measuring device capable of reducing the influence of the nonlinearity of a beam supporting an oscillator.
2. Description of the Related Art
An acceleration-and-angular velocity measuring device disclosed in JP-A 2004-4127 and a self-diagnosing measuring device disclosed in WO 2006/082128 are examples of an angular velocity measuring device provided with an oscillator having a predetermined mass and capable of oscillating at a predetermined frequency, and capable of exerting external force on the oscillator to cancel out a displacement caused by Coriolis force
Enhancement of Coriolis force and sensitivity to the highest possible extent, reduction of noise component to the lowest possible extent and improving the S/N ratio are problems with the oscillation type angular velocity measuring device. The acceleration-and-angular velocity measuring device disclosed in JP-A 2004-4127 is designed to improve the S/N ratio through the synchronous detection of a measured displacement of the oscillator caused by Coriolis force. The self-diagnosing measuring device disclosed in WO 2006/082128 is provided with a servomechanism that reduces displacement caused by Coriolis force to zero. The self-diagnosing measuring device is designed to improve the S/N ratio through the synchronous detection of the output of the servomechanism. Although this prior art can reduce the noise component by synchronous detection, the prior art failed in taking measures for improving sensitivity into consideration.
The sensitivity of the oscillation type angular velocity measuring device to angular velocity can be enhanced by increasing the amplitude of oscillation of the oscillator. However, when the amplitude of oscillation of the oscillator is increased, the oscillation of the oscillator is distorted and saturation of oscillate amplitude or asymmetric oscillation occurs due to the nonlinearity of a beam supporting the oscillator. The distortion of the oscillation of the oscillator distorts the Coriolis force produced by the oscillation of the oscillator and a Coriolis force having a harmonic component is produced.
The acceleration-and-angular velocity measuring device disclosed in JP-A 2004-4127 detects only the oscillation of the predetermined frequency of the oscillator by synchronous detection and feeds back only a component of a predetermined frequency of the oscillation of the oscillator to reduce the oscillation of the predetermined frequency to zero. Thus, a harmonic component is not fed back. Consequently, the instability of a control system is enhanced and measurement error increases. Therefore, there is a limit to the increase of the amplitude of the oscillation of the oscillator.
In the self-diagnosing measuring device disclosed in WO 2006/082128, the servomechanism reduces the displacement of the oscillator caused by the Coriolis force to zero. However, there is a limit to the increase of gain of the servomechanism and there is a limit to the response characteristic because the oscillator has a resonance characteristic. When the amplitude of the oscillation of the oscillator is increased to improve sensitivity, the feedback control of the harmonic component of the Coriolis force due to the nonlinearity of the beam does not function and measurement error increases. Thus, there is a limit to increasing the amplitude of the oscillation of the oscillator.